telecom Flashcards
what are the transmission mode
- Broadcasting which involves the use of a single powerful transmitter and
numerous receivers that are relatively inexpensive to build; example: radio and
television. - Point-to-point communication in which the communication process takes place
over a link between a single transmitter and receiver. In this case, there is usually a
bidirectional flow of information signals which requires the use of a transmitter
and a receiver at each end of the link; example: telephone and a link between an
earth station and a robot navigation the surface of another planet.
what are the transmission moes
- Simplex: information is sent in one direction. Examples are Radio or TV
broadcasting. - Half duplex: information is sent and received on the same channel but not at the
same time. Examples are: Walky Talky, Bluetooth data transfer between two
laptops, etc… - Full duplex: information is sent and received at the same time over two separate
channels. The telephone is an example of full duplex communication.
why do we use digital communications
easy to regenerate distorted signals
easier and more efficient to multiplex several signals
can combine difference signal types
what are the transmission
mediums
guided:
twisted pair, coaxial cable, fiber optic
UTP cable, stp cablecable
unguided
radio waves, microwaves
what is the difference between coaxial and STP
STP uses a foil shield while while coaxial uses a plastic insulation
what are the components of a fiber optic cable
jacket
strengening material
buffer
cladding
core
what are the types of fiber optic cables
single mode
used for long distances
4-5 times more expensive than multimode
core has a smaller radius
uses a lazer as a light source
handling or manufacturing is much harder
less degradation of signals
can carry singals at much greater speed
multimode
what is a PSTN
the public switched telephone network is an overall telecom network consisting of local networks interconnected by one or more long distance networks
what are the satellite services
fixed satellite services (FSS)
broadcast satellite services (BSS)
Mobile satellite service (MSS)
Inter Satellite service (ISS)
what is a molniya orbit
highly or extremely eliptical orbit
what are the 3 segments of a GPS system
Space segment (ss)
control segment (CS)
User segment (US)
what are the 3 entities of a control segment
Master control system
monitor stations
ground antennas
what do antenna noise
temperature Td depend on?
loss between the antenna and receiver input
sky noise from the galaxy, sun and moon
absorption by amospheric gases and precipitation
radiation from the earth into the backlobes of the antenna
interference from man made radio sources
how do you get rid of antenna noise
by placing a metallic rim around the edge of the parabolic dish
what are the atmospheric effects on microwaves
absorption
refraction
diffraction
what is a microwave link
A (terrestrial) microwave link uses a beam of radio waves in the
microwave frequency range to transmit information between two fixed
locations on the earth.
what is frequency reuse
in the context of polarization, same frequency channels can be reused by passing one horizontal and one vertical signal through it
what are the two types of towers and when is each one used
self supporting : relatively short towers
guyed towers: for relatively long towers or when there is no space at the base
what is refraction
refraction is the bending of the radio waves due to changes in the atmosphere (temperature/density/altitude)
describe the condition with respect to n1, n2, and k
if n1 > n2 => Good Condition
if n2 > n1 => Bad condition
if K < 0 => Good Condition
if 1 < k < 0 => Bad Condition
if k > 0 => Good conidtion
if k -> inf => Good condition
what is ducting
atmospheric refraction sometimes traps microwave beams in a waveguide called ducting
what are the components of a setellite
command antenna
broadcast antenna
radio transmitters and receivers
rocket fuel
rocket thrusters
main rocket
camera
solar panels
what is a FSS
a fixed satellite station supports telecommunication services between antennas (satellite and ground station)
what is a BSS
a broadcast satellite station uses a high powered beam to transmit radio or television services right to the end user (Simplex)
what is a MSS
a mobile satellite service provides telecommunication services but move rather than remain stationary
what is a ISS
inter satellite service is used in low or medium orbit to interconnect multiple high orbit satellites constellations
what are the two types of communicating satellites
passive: frequency repeating (RF) repeater satellite (Bent pipe)
active: processing satellite (used for digital) demodulates the uplink signal, provides error correction and retransmits the signal back to earth
what are the 4 advantages and disadvantages of LEO
advantages
less transmission path loss
less transmission delay
lightweight, compact and low cost antennas
people can go up, and down in a short time
disadvantages
large number of satellites to create a global contellation network
mode difficult controls, complex billing and authentication’
cannot constantly point the antenna at an area because the space craft is constantly moving
large earth gravity on them, 7 year total lifetime
what are the 1/3 advantages and disadvantages of MEO
advantages:
provides global coverage with less transmission times and delay then LEO
disadvantage
more satellites than a GEO
system must be deployed and operated in full as a complete network unlike a GEO which can be its own network
de-orbiting requires a great amount of thruster fuel
what are the 2 advantages and disadvantages of GEO
advantage
relatively easy to maintain in orbit for about 15-20 years
raised out of orbit at end of life hence spending less fuel
disadvantage
for mobile, it requires high beam power and aperture radius for reliability
each satellite is bigger more complex and expensive to manufacture
what is the altitude and period of a gps satellite
20200km above surface with a period of 12 hours
what are the components of a GPS user segment
an antenna tuned to the frequency used by the satellite
a receiver processor
highly stable clock
what is the total path lost from base station to a satellite a sum of?
free space loss
atmospheric absorption
ionospheric absorption
rainfall loss
what is transmission
the transfer of a signal, message or any other information from one location to another
what is the difference between analog systems and digital systems
analog systems convert analog messages to signals while digital convert bits into signal
what is modulation
is the process of impinging useful information onto the carrier. it involves varying some parameters of the carrier wave according to the message wave
what are the components of a coaxial cable
jacket
braided copper shield
plastic insulator
copper conductor
